1. Field of the Invention
The invention relates to bicycle drive mechanisms, and in particular to a chainless drive mechanism for transmitting the pedal actuated driving force to the rear wheel. More particularly, the invention relates to a chainless bicycle drive mechanism using a rotatable drive shaft having a shiftable transmission gear system for changing the drive or gear ratio, which includes a coaster mechanism external of the rear wheel axle.
2. Description of the Prior Art
Multispeed bicycles have become ever increasingly popular in the past several years and are accounting for a large portion of bicycle sales. The speed advantages and ease of operation of these multispeed bicycles are some of the main factors increasing their popularity. The most common multispeed transmission for these bicycles is the derailleur gear chain drive system. The derailleur chain drive system comprises a plurality of sprockets of various sizes mounted on the rear wheel shaft in combination with a shifting mechanism which causes the chain to move from one sprocket to another, together with a spring actuated device to adjust and maintain the correct tension in the chain. The various sizes of the drive sprockets provide for the selection of a desired gear ratio depending upon the particular terrain over which the bicycle is being driven.
Such derailleur systems, however, are relatively expensive, complex and are subject to substantial maintenance problems due to the use of a chain and the continual movement of the chain between sprockets to achieve the desired gear ratio.
Another type of multispeed drive mechanism for bicycles is known as the "chainless" type. This mechanism uses a shaft instead of a chain for transmitting the pedal actuated driving force to the rear wheel. Various types and arrangements of chainless bicycle drive mechanisms have been developed in the past which use such drive shafts for transmitting the driving force supplied by an operator through the pedal actuated crankshaft to the rear wheel. Many of these mechanisms use expensive bevel or angled gears which intermesh with ring gears mounted on the rear wheel axle or pedal crankshaft. Examples of such prior mechanisms are shown in U.S. Pats. Nos. 479,470, 506,685, 589,266, 614,969, 624,964, 649,878, 1,334,108 and 2,378,634.
These mechanisms also are provided with means for shifting the intermeshing gears selectively into engagement with a selected ring gear to affect the gear change or speed ratio adjustment. Another known type of chainless multispeed bicycle drive mechanism is shown in U.S. Pat. No. 3,863,503, which uses an axially adjustable two piece drive shaft having gears on the ends thereof, which gears selectively engage concentric gear teeth formed on a pair of front and rear discs.
Various problems exist with such known constructions in that the concentric gear rings or teeth on the discs are expensive to produce since they require elaborate machining and manufacturing procedures. Likewise, the intermeshing gears are of the expensive beveled or angled type which further increases the cost of the bicycle.
One of the main disadvantages of known chainless bicycle drive mechanisms, with or without gear ratio changing ability, is the coaster mechanism which permits the bicycle to coast freely upon stopping of the pedal action. Many of the mechanisms set forth in the patents listed above require a manual manipulation to be performed by the operator to disengage the meshing gears when starting to coast in order to stop rotation of the drive shaft and to enable the rear wheel to continue to rotate freely upon stopping of the pedal movement. In order to eliminate this problem, mechanisms such as shown in U.S. Pat. No. 3,863,503, continue to utilize a pressure sensitive ratchet arrangement mounted within the hub of the rear wheel. This arrangement is a standard component on most single or multispeed bicycles in use today, but again increases the cost and maintenance of the bicycle.
Therefore, the need has existed for a chainless bicycle drive mechanism having a variable speed and gear changing arrangement, the components of which can be produced inexpensively without expensive machining operations, which permits the bicycle to "free coast" without any manual operation or gear changing being required by the operator and without the use of a pressure sensitive ratchet arrangement within the rear hub, and which automatically stops the rotation of the front disc and connecting drive shaft upon stopping of the pedal motion, without affecting the continued rotation of the rear wheel and free coasting of the bicycle. No known chainless bicycle drive mechanism of which I am aware provides these features in a simple, relatively inexpensive and rugged mechanism.